In recent years, from the viewpoint of environmental protection, efforts to aim at carbon neutrality have proceeded. Among these efforts, in the chemical industry, attention is focused on biopolymers made from biomass resources. Among biopolymers, polylactic acid is made from an agricultural product, and therefore is excellent in terms of cost and the like, and is put to practical use in various applications. But, a disadvantage of the polylactic acid is that its molecular structure is rigid, and therefore its molded article is hard and brittle.
In order to solve such a disadvantage, attempts are made to convert polylactic acid into various block polymers.
For example, in Patent Document 1, a polylactic acid block copolymer obtained by linking a crystalline segment consisting of a substantial homopolymer of poly-L-lactic acid or poly-D-lactic acid and an amorphous segment comprising L-lactic acid and D-lactic acid as main components is proposed.
In Patent Document 2, a block copolymer in which a polylactic acid segment and a vinyl-based polymer segment are linked at a copolymerization ratio of 99/1 to 1/99 parts by weight is proposed.
In Patent Document 3, a polylactic acid-based block copolymer having segments consisting of L-lactic acid units at both ends of a segment mainly comprising an aliphatic carbonate unit via segments consisting of D-lactic acid units is proposed.